New Transition-State Models and Kinetics of Elimination Reactions of Tertiary Alcohols over Aluminum Oxide

Abstract

A new transition-state model was developed in order to justify the anti intramolecular E2 elimination with cis (Z)-preference over pure alumina and intermolecular E2 elimination with trans (E)-preference over doped alumina. The reactions of model compounds 1,2,3-triphenyl-2-propanol (1), 1,2-diphenyl-2-propanol (2), and 3,3,3-trideuterio-1,2-diphenyl-2-propanol (3) with aluminum oxides with a pH range of 4.5−9.5 and thorium oxide in the temperature range of 200−350 °C in 2-hexanol have been investigated. Over acidic alumina (pH = 4.5 ± 0.5), the ratio of E-isomer to Z-isomer (E/Z ≅ 2) for 2 was found to remain unchanged in this temperature range. At 300 °C, however, Saytzeff elimination favored Hofmann. Over pure alumina the E/Z ratio was equal to 0.650 (2-alkene/1-alkene = 0.750). At equilibrium, the E/Z ratio for 2 was equal to 4.5 with the formation of trace amounts of Hofmann adducts. The ratio of Saytzeff to Hofmann elimination was found to be pH independent. Any decrease in pH caused a slight increase in the E/Z ratio. The average primary kinetic isotope effect (k H/k D) for elimination at 230 °C was equal to 3.775 ± 0.227. The ratio of E/Z over thorium oxide at 300 and 350 °C was similar to that of aluminum oxide at 300 °C, but the Saytzeff elimination was surprisingly favored over Hofmann! The energy of activation (E a), entropy of activation (ΔS ⧧), selectivity, isotope effect (k H/k D), and semiempirical calculation (AM1) all agreed with concerted E2 elimination.

Nickel-Catalyzed Direct Synthesis of Aryl Olefins from Ketones and Organoboron Reagents under Neutral Conditions

“…This indicates that the loss of the hydrogen (or proton) from the carbinol is not rate-limiting in the catalytic process. 13 Nickel(0) complexes of phosphines easily form oxanickelacycles A with both aldehydes and ketones (Fig 5f). 14 Oxanickelacycles were implicated as key intermediates in some catalytic processes, 15 including 1,2-addition of organoborons to carbonyl groups that resulted in carbinols.…”

An XRD and Fourier-transformed infrared spectroscopy investigation of single and mixed γ-alumina and thorium oxide

“…␥-Alumina was prepared by hydrolysis of aluminum isopropoxide [Al(OC 3 H 7 ) 3 ] at room temperature; it was heated at 120 • C for 24 h to remove excess water followed by calcinations at 600 • C for 6 h. Thorium oxide was prepared through calcination of thorium nitrate [Th(NO 5 ) 4 ·4H 2 O] at 600 • C for 6 h [28]. Mixed ␥-alumina and thorium oxide were prepared with various compositions (100, 95, 90, 80, 50, 25, 15, 5 and 0 wt% Th, respectively) by addition of a solution of thorium nitrate to a slurry of aluminum hydroxide [Al(OH) 3 ] in deionized water at ambient temperature.…”

“…Dabbagh and Mohammad Salehi constructed new transition state models for the elimination reactions of alcohols over aluminum oxide [28]. They depicted the formation of pure ␥-alumina from aluminum hydroxide as a polymerization process.…”

Ab initio and semiempirical conformational and configurational analysis of N-2-(1,4-dioxane)-N’-(4-methylbenzenesulfonyl)-O-(4-methylphenoxy)isourea

“…The conformational geometry of the transition and/or intermediate states of these compounds has been documented to establish the selectivity of the chemical reactions and/or the stereochemistry of their *Corresponding author. E-mail: dabbagh@cc.iut.ac.ir adducts [43][44][45]. Since it is entirely conceivable that the pharmaceutical activity of dioxane is related to the physicochemical properties, thorough investigation of 1,4-dioxane derivatives was initiated many years ago .…”